Divert-air valves for the recirculation of compressed fresh gas, optionally with recirculated exhaust gas, from the pressure side of a compressor of a turbocharger back to the suction side of the compressor, have previously been described. The connection between the pressure side and the suction side of the compressor via a bypass line is required for the transition from a high load into the propulsion operation of the internal combustion engine to prevent a high conveyance of the booster pump against a closed throttle flap and the resultant pumping effect, and to prevent a sudden drop of the turbo speed which is too strong with resulting thermodynamic problems.
Divert-air valves are frequently operated electromagnetically, wherein the valve closure body of the valve is moved via the armature by the electromagnetic force and can be lowered onto a valve seat and be lifted off therefrom, the valve seat being arranged in a flow housing between an inlet and an outlet of the compressor. Very fast switching is required in these divert-air valves because of the rapidly changing load conditions of the compressor. Most divert-air valves are therefore designed for equalized pressure. This is accomplished by providing openings in the control body via which the pressure applied to the control body from below will be conducted into the interior of the valve, wherein the effective diameters on both axial sides of the control body are also selected to be equal. The control body will consequently be acted on only by the force of a spring that is effective in the closing direction and by the force of the electric magnet that is effective in the opening direction. Very short opening and closing times are achieved thereby, provided that the design has been correctly implemented.
Such a valve is described, for example, in EP 1 941 138 B1. The electromagnetic actuator of this divert-air valve is surrounded by a plastic housing which bears against a connection housing accommodating the control body in its interior. A groove is formed on the connection housing between these two housings, the groove being adapted to have a sealing ring placed therein so that no gas that is present in the interior can leak to the outside through the gap between the housings. The actuator housing, with interposition of a sealing ring, also bears against a flow housing in which the duct is formed that connects the inlet and the outlet of the compressor. Problematic in such a valve is, however, that the coil is not sufficiently protected from ingress of the gas conveyed by the compressor that contains contaminants and oil. This gas may happen to enter the coil along the armature between the sliding sleeve and the coil carrier and between the return plate and the coil carrier and, between the two housings, it may also axially intrude into the region between the two sealing rings. This will result in an increased risk of corrosion on the coil. The individual components also must be mounted, and a disturbing noise will be generated during the opening of the valve when the control body abuts against the actuator housing.